Table 1 presents the demographic characteristics of the participants. Of the 1483 participants, the mean age was 69.6 ± 5.7 years and 66.35% were female. The highest frequency of sleep duration was 6h per day, accounting for about 30% of the participants. People with moderate sleep duration (6-7h, per night) were more likely to be younger on average, have better education and have good cognitive scores. People with short sleep duration (≤ 5 hours) were more likely to be female, have a history of diabetes, arrhythmia, hearing problem, cataract, and depressive symptoms. People with long sleep duration (≥ 8 hours) were more likely to suffer from coronary disease, and they more often smoked.
Table 1
Characteristics of study participants by Sleep Duration
Characteristics | Total Sample | Sleep duration (hours) |
≤ 5 | 6 | 7 | ≥ 8 | p |
N (%) | 1483 | 384 | 437 | 280 | 382 | |
Age | 69.6 ± 5.7 | 70.5 ± 5.6 | 69.2 ± 5.6 | 69.0 ± 5.4 | 69.5 ± 5.9 | 0.001 |
Female sex | 984 | 282(73.4) | 281(64.3) | 171(61.1) | 250(65.4) | 0.004 |
Marital status | | | | | | 0.144 |
Married | 1216 | 303(78.9) | 371(84.9) | 236(84.3) | 306(82.0) | |
Unmarried | 2 | 2(0.5) | 0(0) | 0(0) | 0(0) | |
Divorced | 6 | 2(0.5) | 1(0.2) | 2(0.7) | 1(0.3) | |
Widowed | 259 | 77(20.1) | 65(14.9) | 42(15.0) | 75(19.6) | |
Educational levels | | | | | | 0.004 |
Illiteracy | 523 | 166(43.2) | 134(30.7) | 102(36.4) | 121(31.7) | |
Primary school | 625 | 139(36.2) | 193(44.2) | 114(40.7) | 179(46.9) | |
Junior high school or above | 335 | 79(20.6) | 110(25.2) | 64(22.9) | 82(21.5) | |
Current smoking | 162 | 33(8.6) | 45(10.3) | 44(15.7) | 40(10.5) | 0.076 |
Current drinking | 176 | 25(6.5) | 59(13.5) | 37(13.2) | 55(14.4) | 0.002 |
Hypertension | 764 | 191(49.7) | 225(51.5) | 151(53.9) | 197(51.6) | 0.768 |
Diabetes | 321 | 93(24.2) | 95(21.7) | 48(17.1) | 85(22.3) | 0.177 |
Hyperlipidemia | 446 | 135(35.2) | 119(27.2) | 83(29.6) | 109(28.5) | 0.077 |
Coronary heart disease | 259 | 80(20.8) | 80(18.3) | 49(17.5) | 50(13.1) | 0.040 |
Heart failure | 91 | 29(7.6) | 21(4.8) | 19(6.8) | 22(5.8) | 0.395 |
COPD | 198 | 60(15.6) | 59(13.5) | 30(10.7) | 49(13.6) | 0.321 |
Stroke | 73 | 23(6.0) | 16(3.7) | 12(4.3) | 22(5.8) | 0.357 |
Brain trauma | 38 | 11(2.9) | 8(1.8) | 8(2.9) | 11(2.9) | 0.722 |
Hypothyroidism | 35 | 12(3.1) | 7(1.6) | 13(4.6) | 3(0.8) | 0.006 |
Cataract | 288 | 86(22.4) | 84(19.2) | 43(15.4) | 75(19.6) | 0.161 |
Hearing problem | 325 | 106(27.6) | 96(22.0) | 51(18.2) | 72(18.8) | 0.020 |
BMI | 25.8 ± 3.3 | 25.7 ± 3.2 | 25.8 ± 3.2 | 25.6 ± 3.6 | 26.1 ± 3.4 | 0.271 |
GDS | 3.0 ± 2.6 | 3.5 ± 2.9 | 3.2 ± 2.4 | 2.9 ± 2.7 | 2.5 ± 2.3 | < 0.001 |
MMSE scores | 27.9 ± 2.9 | 27.7 ± 2.9 | 28.3 ± 2.4 | 28.1 ± 2.6 | 27.7 ± 3.5 | 0.001 |
*The P value represents the test for difference in characteristics between participants in different sleep duration groups based on the analysis of variance or chi-square test as appropriate.
As shown in Table 2, the linear regression analysis showed that, compared to participants with 6-hour sleep duration per night, those with short sleep duration (≤ 5h) and long sleep duration (≥ 8 h) had significant lower cognitive scores (adjusted R2 = 0.01, F = 5.64, p < .001). After adjusting for all covariates, the association between long sleep duration and worse cognitive function remained significant, adjusted R2 = 0.18, F = 17.89, p < .001.
Table 2
β coefficient (95% confidence interval) of MMSE score associated with sleep duration from general linear regression models
| No. | | β coefficient (95% confidence interval), MMSE score |
Sleep duration | Participants | | Model 1* | Model 2** | Model 3*** |
≤ 5h | 384 | | − .66(-1.94, − .26) | − .27(-.64, − .10) | − .25(-.62, .11) |
6h | 437 | | 0.00 (Ref.) | 0.00 (Ref.) | 0.00 (Ref.) |
7h | 280 | | − .18(-.62, 0.25) | − .10(-.50, 0.30) | − .14(-.55, .25) |
≥ 8 h | 382 | | − .69(-1.09, − .29) | − .61(-.98, − .24) | − .67(-1.04, − .29) |
Model 1*: unadjusted; Model 2**: adjusted for age, gender, levels of education, ever smoking and alcohol consumption; and model 3*** was additionally adjusted for hypertension, diabetes, hyperlipidemia, coronary disease, heart failure, COPD, hypothyroidism, brain trauma, hearing problem, cataract and depressive symptoms scoring.
Table 3 presents the association between sleep duration and cognitive impairment. ORs (95% CI) of cognitive impairment are presented for short and long sleep duration compared to the mid-range sleep duration category. In the unadjusted models, participants who had short sleep duration had a 2.32-fold increased likelihood of cognitive impairment (OR = 2.32 [95% Cl 1.49, 3.62]), and long sleepers had a 74% increased risk compared to participants with normal sleep duration (OR = 1.74 [95% CI 1.10, 2.76]). After adjustment for all confounders, the odds ratios were 1.66 (1.02, 2.70) and 1.77 (1.07, 2.92), respectively.
Table 3
Odds ratio (95% confidence interval) of cognitive impairment associated with sleep duration from logistic regression models
Sleep duration | No. Participants | Model 1* | Model 2** | Model 3*** |
≤ 5h | 384 | 2.32(1.49, 3.62) | 1.75(1.09, 2.81) | 1.66(1.02, 2.70) |
6h | 437 | 1.00 (Ref.) | 1.00 (Ref.) | 1.00 (Ref.) |
7h | 280 | 1.16(0.67, 1.99) | 1.12(0.63, 1.99) | 1.15(0.64, 2.06) |
≥ 8h | 382 | 1.74(1.10, 2.76) | 1.75(1.07, 2.88) | 1.77(1.07, 2.92) |
Model 1*: unadjusted; Model 2**: adjusted for age, gender, levels of education, ever smoking and alcohol consumption; and model 3*** was additionally adjusted for hypertension, diabetes, hyperlipidemia, coronary disease, heart failure, COPD, hypothyroidism, brain trauma, hearing problem, cataract and depressive symptoms scoring.
The relationship between sleep duration and each of the cognitive subdomains was analyzed using linear regression models. As shown in Table 4, the unadjusted model (Model 1) suggested that individuals reporting short (≤ 5 h) or long (≥ 8h) sleep duration per night had a significantly higher risk of attention and calculation impairments than the reference group (6 h) (All p < 0.05). even adjusted for all covariates, significant greater associations between short (≤ 5 h)/long (≥ 8h) sleep duration and low attention and calculation scores. In the crude model and after adjusting for the all covariates, it was found that long sleep duration led to poor orientation (p < 0.05). The same results also found that long sleep duration was associated with lower scores of delayed recall and linguistic competence (p < 0.05).
Table 4
β-coefficient (95% confidence interval) of cognitive domain score associated with sleep duration from general linear regression models
Cognitive domain | Sleep duration | Model 1* β (95% CI) | Model 2** | Model 3*** |
Orientation | | | | |
| ≤ 5h | -0.15(-0.28, -0.02 | -0.05(-0.18, 0.06) | -0.05(-0.18, |
| 6h | 0.00 (Ref.) | 0.00 (Ref.) | 0.00 (Ref.) |
| 7h | -0.08(-0.22, 0.05) | -0.07(-0.20, 0.06) | -0.07(-0.21, 0.06) |
| ≥ 8 h | -0.15(-0.28, -0.02) | -0.13(-0.26, -0.00) | -0.12(-0.25, 0.002) |
Immediate recall | | | | |
| ≤ 5h | 0.00(-0.01, 0.01) | 0.22(-0.01, 0.01) | 0.00(-0.00, 0.01) |
| 6h | 0.00 (Ref.) | 0.00 (Ref.) | 0.00 (Ref.) |
| 7h | -0.00(-0.01, 0.01) | -0.00(-0.15, 0.01) | -0.00(-0.01, 0.01) |
| ≥ 8 h | -0.01(-0.02, 0.00) | -0.01(-0.02, 0.00) | -0.01(-0.02, 0.00) |
Attention and calculation | | | | |
| ≤ 5h | -0.36(-0.53, -0.19) | -0.22(-0.39, -0.06) | -0.21(-0.38, -0.05) |
| 6h | 0.00 (Ref.) | 0.00 (Ref.) | 0.00 (Ref.) |
| 7h | 0.04(-0.23, 0.14) | -0.02(-0.20, 0.15) | -0.03(-0.21, -0.14) |
| ≥ 8 h | -0.24(-0.42, -0.07) | -0.21(-0.38, -0.05) | -0.22(-0.38, -0.05) |
Delayed recall | | | | |
| ≤ 5h | -0.03(-0.11, 0.04) | -0.01(-0.08, 0.06) | -0.00(-0.08, 0.07) |
| 6h | 0.00 (Ref.) | 0.00 (Ref.) | 0.00 (Ref.) |
| 7h | -0.02(-0.10, 0.06) | -0.01(-0.10, 0.06) | -0.02(-0.10, 0.06) |
| ≥ 8 h | -0.09(-0.17, -0.01) | -0.08(-0.16, -0.01) | -0.08(-0.16, -0.01) |
Linguistic competence | | | | |
| ≤ 5h | -0.09(-0.20, 0.01) | -0.02(-0.13, 0.08) | -0.01(-0.11, 0.09) |
| 6h | 0.00 (Ref.) | 0.00 (Ref.) | 0.00 (Ref.) |
| 7h | -0.03(-0.15, 0.08) | -0.02(-0.13, 0.09) | -0.02(-0.14, 0.09) |
| ≥ 8 h | -0.17(-0.28, -0.06) | -0.15(-0.26, -0.04) | -0.15(-0.26, -0.05) |
Special and drawing | | | | |
| ≤ 5h | -0.05(-0.12, 0.01) | -0.00(-0.06, 0.06) | -0.00(-0.06, 0.06) |
| 6h | 0.00 (Ref.) | 0.00 (Ref.) | 0.00 (Ref.) |
| 7h | 0.00(-0.07, 0.07) | 0.01(-0.05, 0.08) | 0.00(-0.06, 0.07) |
| ≥ 8 h | -0.03(-0.10, 0.03) | -0.02(-0.09, 0.04) | -0.02(-0.08, 0.04) |
Model 1*: unadjusted; Model 2**: adjusted for age, gender, levels of education, ever smoking and alcohol consumption; and model 3*** was additionally adjusted for hypertension, diabetes, hyperlipidemia, coronary disease, heart failure, COPD, hypothyroidism, brain trauma, hearing problem, cataract and depressive symptoms scoring.